Worm making process



Nov. 22, 1932. w' F. ZIMMERMANN 1,883,782

WORM MAKING PROCESS Original Filed Jan. 28, 1921 6 Sheets-Sheet 1 Nov.22, 1932.

, W, F. ZIMMERMANN WORM MAKING PROCESS Original Filed Jan. 28, 1921 6heets-Sheet 2 Eiwuewtoz' Nov. 22, 1932.

w. F. ZIMMERMANN WORM MAKING PROCESS e Sheets-Sheet 3 Original Filed Jan28, 1921 mj um :ut

i vm Q3630 wbd Nov. 22, 1932. w.- F. ZIMMERMANN WORM MAKING PROCESS 6Sheets-Sheet 4 Original Filed Jan. 28, 1921 00 0 +0 nx 0 3% m ammo;

WEEK I ta Nov. 22, 1932- W.IF. VZIMMERMANN WORM MAKING PROGES S OriginalFiled Jan. -2s, 1921 e Sheets-Sheet 5 2315 .vook

/ 31mm s y-k Nov. 22, 1932. w. F. ZIMMERMANN WORM MAKING PROCESSOriginal Filed Jan. 28, 1921 6 Sheets-Sheet 6 G t I Patented Nov. 221932 UNITED STATES PATENT oFFicfE WILLIAM F. ZIMMERMANN, OF MAPLEWOOI),NEW JERSEY, ASSIGNOR TO,GOULD &

EBERHARDT, OF NEWARK, NEW JERSEY, A CORPORATION OE NEW JERSEY i WORMMAKING rnocnss Original application filed January 28,1921, Serial No.440,782, new Patent No. 1,430,485, dated September 26, 1922. Divided andthis application filed April 1, 1922. Seria1No. 548,722.

This invention deals with the production of helical groovesby theprogressive cutting action of a hob and it seeks to eliminate or renderinconsequential certain inaccuracies created by reason of a heretoforeunavoidable incompatibility between the actual contours and locations ofthe cutting edges of the hob and the sought-for contour of the helicalgroove. This case is a division of my application Serial No. 440,782filed January 28, 1921, which has matured into Patent. No. 1, i30,485dated Sept-ember 26, 1922.

' It has been demonstrated that the ultimate efiiciency, smoothness ofaction, and maintenance of a so-called worm-drive very materiallydepends upon the pressure-angles, contour and finish of the drivingsurface of the worm; this surface being represented by" the face orfaces, of the helical groove, or

grooves, formed by the threads or teeth of the,

worm. 'Such a face, geometrically considered, is a warped surfaceproduced by a generatrix revolving about and simultaneously translatingin the direction of a directrix which may be regarded as the axis of theworm. In the case of a worm corresponding to a straight-sided rack, thegeneratrix is a strai ht line, but in other cases, it may be a linecurved either in a plane or in a space of three dimensions. Forinstance, some designers have advocated a hyperbolic contour (inlinear-section) on the supposition that it affords a maximum of rollingcontact'and a minimum of sliding contact with the tooth of theworm-wheel.

Such worms may be laboriously cut in a lathe by means of a lathe-toolhaving its outtingedge conforming to the contour of the linear-section,but the production of worms in that manner is too costly and irksome tosatisfy commercial demands. Consequently, many attempts have been madeto adapt the hobbing-process (long successfully used for making helicalgears) for the generation of worms Such efl'orts have heretoforeproduced only indifferent results for reasons either not clearlyunderstood or because of errors non-rectifiable within the skill of theart.

An analytical investigation of this subject mating V is an extremelyoperose matter owing to the abstruseness of the factors and relations.in-

volved. Attempts to ascertain the theoretical shapes and dispositions ofthe contours'o'f the cutting-edgesof' the hob, by a mathematicalanalysis based on differential and'integral calculus, haveled only tolengthy difi'eren' tial equations incapable of solution save by undulylaborious successive approximations and the curves derived therefromareincapable of being accurately reproduced by any practical method ofmaking and grinding hobs. In fact, the purely theoretical discussions ofthis sub ect are stillin controversy among the experts in this art.

.Ihave, however, succeeded 1n. discovering a practical method of soforming a hob as to enable it to be used as a means instrumentalinsuccessfully processing a worm truly conforming to any predeterminedtooth-contour. This method is at once simple, essentially practicable,and capable of yielding a hob perfectly conforming to all requirements.This hob differs from any heretofore produced in that its cutting-edgesare so con.- toured and so disposed as to be entirely cam patible withthe groove-contour selected for theworm to be manufactured.-

If the peripheryof a circular be given I a contour accuratelycomplementary to a circular groove, and if it be interfitted with saidgroove, the'lineof contact will wholly lie in an axial'plane' But if thegroove be helical, instead of circular, the" contour of.

come intoaction successively on the blank,

theymay in the aggregate form som'e other continuous (or dis-continuous)line, providing that all portions of such other line are circularprojections of thefundamental contour. The actual cutting-edge may thusbe made continuous. Likewise, thecircular pro- V series of elementalcutting edges; since their circular pro ect1'ons will always reduce themto the basic-line. We are, therefore, at liberty to select the plane ofour actual cutting-edge providin it is derived from the lineof contactaforesaid; otherwise an interference will be encountered and thedisk-cutter will fail to produce the contour, aimed at in the'blank.

It is more convenient, as a matter of, practical 'mechanics, to employ acontinuous cutting edge lying wholly'in a given plane; as for example,on-e taken in linear section, or one taken; at right angles to thethread. In the latter case, the undistorted shape of the-contourwillrepresent the normal section of the thread. It will, however, be,seen from the foregoing -that this plane does not represent the regionof cutting-action of the successive portions of the cutting-edge, sincesuch portionshave their actual operative effects "only when incoincidence with the aforesaid basic contour line which, as explained,occupies a space of three dimensions.- It followsthat, by making thenormal section of each tooth of a'disk-cutter conform to the circularprojection of the basic contour, we

can successfully cut a helical groove of any desired contour; providingit has noundercut. a I

But a section thus derived and quite ade I quate for allthe teeth of adisk-cutter would not answer for the successive teeth of a helicalcutter since the-accumulative lateral displacement created by the driftof the helix should, to avoid interference, proceed from a fundamentalcontour of contact'materially different from that characteristic oftherelation between the same worm and a disk-cutter. Likewise, if weshould attempt to makethe normal section of the helix of the hobcontinuously complementary to the normal sec tion of the helix oftheworm, or similarto the sectionemployedfor the (llSlC-CLllEtQl,WVQ wouldencounter a pronounced interference due to the fact that the helicallocus of such section does not coincide with the theoreticah ly correcthelical locus obtained by using the contour of contact as a .generatrix,but is displaced in such a direction as will conflict with the wall thatwould be produced-in-the worm by the cutting action of a theoreticallycorrect locus, assuming its surface to present an infinite number ofteeth. If we should neglect all but short length of the aforesaidcuttingrhelix then we would avoid perceptible interference, but with theconsequence that the few teeth representing the skeleton of that shortlength would have to do all the cutting somewhatin analogyto the burdencarried by the sin-gle tooth of afiy-cutter, and a hob-so 65.. formedwould be inadequate to meet the commercial requirements of worm-cutting.We require the action of many teeth, and consequently need to use ahelix of at least one or more convolutions. And, accordingly, the teeth,or, more properly speaking, the cuttingedges (excepting those beyond theregion of interference) must all fall within the helical coidsuflicientlyto, avoid any untoward interference. I

A primary purpose of this invention is,

therefore, to develop an asymetrical helical locus for the successivecutting-edges of the hob which will enable it successfully and withoutany undercutting (due to interfer 'ence) accurately to produce a truewormhaving any desired thread outline, either straight-sided orotherwise. Also'to developsuch a locus that, from a standpoint ofpractical. mechanics it can be-reproduced by or dinary devices andmethods of shop practice adequately understood by, and within theconstructive capacity of, such mechanics as are available formanufacturing purposes. My method of making a hob of this descriptionmay, for purposesof analysis, besaid to consist in several steps; first,cutting a helix thread having a cross-sectional contour suitablefor therequirements of a fly-cutter; i. e., a cutter having but one tooth orcutting edge; second, ascertaining the dimensions and proportions ofwhat may be termed the path or region of interference of thisv hobthreadwhen conceived to be in working re lation with the true helix of theworm; third,

then precisely determining theform and dimensions of a secondary locusof'truly helical shape which, if subtracted from:the appropriate sideof'the primary helix, would eliminate the normal interference due to thelatter; and fourth, in re-cutting the primary helix; usingthepre-calculated lead and contour of the thus-derived secondary clearance.This invention accordingly proposes an improved process of'continuouslyproducing a single or multiple thread worm, and it also proposes amethod of making a hob capable of being used as a means instrumental incarrying out the worm-making process, and

it also embraces, as a new article of manufacture, a novel hob.

Other objects and part indicated in the following description and inpart rendered apparent therefrom in connection with the annexeddrawings.

To enable others skilled in the art to so fully apprehend the underlyingfeatures advantages will be in hob. Fig. 2 is a perspective thereof.Fig.

3 is a perspective illustrating the hob in the act of cutting a helicalgroove in a blank. Figs. 4 to 12 inclusive are explanatory of thedevelopment of said'hob; Fig. 4 showing the linear section of thepredetermined groove; Fig. 5 showinga transverse projection of thehelical elements of said groove;

Fig. 6 showing a projection in an axial plane of the same togetherwith'the traces of certain auxiliary planes; Fig. 7 showing a viewsimilar to Fig. 5 with the addition of radial development planes and hobellipsis; Fig. 8 showing a development of the relation between the Wormhelixand the 'hob helix; Fig. 9 showing the normal section of a hobtooth derived from Fig. 8; Figs. 10 and 11 showing development of thehob helicoid analogous to the development of Figs. 5 and 6; and Fig. 12showing an assembly whereby. the interferences of the differentpositions progressively assumed by thenormal section of Fig. 9 areaccurately depicted.

The graphical step of driving the intere ference constants can best beexplained by way of a concrete example. Let it be desired acteristics:

' 1.0234 linear pitch 0.9075 normal circular pitch 2.5000 pitch diameter3.0720 outside diameter 4.0936 lead 0.6241 depth to tooth 7 0.4535thickness along normal chord 0.2901 addendum. v

Angle of threadwith axis=62 28 15" Pressure angle in linear direction=Number of threads =4 right-handed.

For determining the interference constants, I preferably resort to agraphical solution, such asthat herein described :-arrived at through anapplication of the principles of descriptive geometry. This has theadvan: tage of being not unduly diflicult and of visualizing theinterference on a magnified scale. The graphical analysis. is superiorto to hob a worm having the following charany physical or mathematicalexamination,

although the latter may be resorted to for the purpose of arriving atthe values from which the lead of the auxiliary helix may be computedInlaying out the successive drawings, when following the graphicalmethod, it is recommended that a scale of say 10:1 be adopted so as toreduce to an inconsequential degree the proportionate effect of suchminor inaccuracies as may be expected in the execution of well-madedrawings.

Let itbe required to cut the above defined H worm by means of a singlethread hob having a given outside diameter of say 4.500.

Its normal circular pitch must, of course, be

identical with that of the worm. Let its depth of tooth be 0.668, itsnor. chord, thickness be 0.4537, and its corr. add. be 0.334,

and its lead be 0.9101, and the angle of its thread with the axis be 435". 7

An accurate enlarged projection of helix of the worm will first bedrawn. It will suffice to obtain'the skeleton of the complete helix, i.e., three line helices representing respectively the rootcircle, thepitch circle, and the outermost circlezofthe thread.

Referring now to Figs. 4 to 12, there will be seen a full disclosure ofmy derivation of the hob helicoid suitable for the given worm. Thecircular arcs a, b and 0, are accurately described by. Fig. 5 torepresent the outside, pitch and root circumferences. These threequadrants in practice will be drawn on the selectedmagnified scale. Thisview reprethe' sents a projection on a plane transverse to the 7 axis ofthe worm. From it is derived a projection on an axial-plane representedby the trace HO by laying-oil" on the base line right and left of thepoint O a distance equal will obtain the projection of the helicoid of 7By a like procedure, is obtainedvv the extension of thisprojection'shown by Figs. 7 and 8 and, similarly the projection of thehelicoid for the hob, shown by Figs. 10 and 11,- is obs tained.

The contour (Fig. 9) suitable for a disk-' cutter is now derived. Aseries of radialplanes are drawn to cut the worm-blank;

the groove of the worm, as shown by Fig.6.

these planes being located by their traces 1r, 1

21', 81", etc. on Figs. 7 and 8. They are located on the walls of thehelicoid of Fig. 8 by projecting over their intersections I with thecircles a and 0 of Fi 7 and drawin strai' 'ht b b t:

lines between the corresponding intersections on the helices a, a b, bcand c these lines being straight in-all projections since the linearsection of this worm is straight-sided.

' paper) may beregarded astheline (Fig;

8) and the'central point is denoted by O.

Now, let us imagine an infinitely thin disk (of the same diameter astheoutside diameter thathas been selected for the hob) to be locatedconcentric with O so as to coincide with the line OQ drawn at the helixangle.

groove.

This disk can be shifted along its axis ac untilithits an adjacent wallof the helicoidal If it'be shifted further, it would cut into said walland create an interference.

. Therefore, thewidth from the center-line of a non inter feringdisk-cutter, measured at its outside diameter, will be equal to theaforesaid shift.

for its minor axis this diameter times the sine of the helix angle ofthe worm. Having drawn this ellipse, as shown by Fig.7 ,1ts1ntersect-ions with the traces 17', 21, 31", etc. are

noted and these are projected over to the corresponding traces on Fig. 8and, of the various new. intersections thus located,.the one nearest tothe line -OQ, is noted; this being the pointmarked G. By likewise takingdifferent diameters, drawing their ellipses on Fig. 7, notingtheintersections, projecting them andtaking the nearest point of eachset,

there is obtained a series of points A,Y, B, C, D, E, F and G on Fig. 8.These points are then projected on to the various diameters; therebyderiving the base contour represented by Fig. 9 which showsthe normalsection of the hob 'cuttingedge suitable for a finishing As has beenexplained, this section is not appropriate for the entire length of thehelix, of the ho-b for the reason that it would, if.

continued, give rise to interferences with the walls of the worm. It,therefore, requires to be progressively. modified and the method ofdetermining the extent and nature of the modification, willnow beexplained.

Referring to Figs. 6 and 11, the helicoid is shown cut by a successionof spaced planes 1 to 19 inclusive. These planes represent thesuccessive relations attained between the above-derlved section and thehellcoidal groove as the blank and hob are relatively rotated; As shown,the line IO"has been divided into twelve equal parts to represent thenumber of teeth which it is deemed advisable to have in one completeconvolution of the hob. In this example, the work is to have fourthreadsand the hob but one and there fore the length 1-0 (which equals'lead) of worm will correspond to the region of action of one revolutionof the hob. It is not necessary to lay out the relation of thetooth-section to the worm in each of the'divig sions and therefore itwill suffice to take every fourth division and draw lines suchas 5, 9

13 and 16 perpendicular to the helix angle of the worm. It is advisable,however, to

draw lines through the lastthree or'four divisions, as indicated by 16,17, 18 and 19 toensure greataccuracy for the last fewcutting edgesinasmuch as they may be usedas finish jections of the outside periphery,the pitch circle, and the'root circle of the worm as cut at an anglewith the axis of-the worm, said lines a, b and 0 are elliptical curves.

Likewise, lines K, L and M represent the section of the hob cut by thesame'pla-ne and, as this plane is likewise at an angle (here a veryslight one) with the axis ofthehob, these lines K, L and M arelikewiseelliptical; the minor axis of the ellipse being equal to theradius ofthe hob andits major axis being equal to said radiusdivided'bythe sine of the angle between said plane and the axis of the hob. i

Having thus laid out these ellipses, the sections taken successivelyperpendicularly to the line on Fig. 6 representing the helix angle, mustbe laid out and properly spaced on the ellipse of the'worm shown by Fig.12. These sections are those indicated by the trace lines O-F 17;13,.T1;3;. 5T5, etc.', on Fig.

6. To lay out section T5, for, example, the 7,

distance from I to N is obtained by measurement from Fig. Gand thislength is laid off on the ellipse a (Fig. 12), starting from the pointI. This locates the point N on the ellipse a. Likewise, the distance IQ,(from F ig. 6) is laid off on ellipse I) (Fig.12),,meas-. uring fromI'fandthis gives the location of the point Q on the ellipse Z). So,also, the

distance IR is ascertained fromFgig. 6 and transferred to F ig, 12; itbeing laid ofi' from the point 1', thereby locating-R on ellipse c.Throughthese points N, Q and R, a smooth curve is drawn and this-givesus'the true pro-- jection of one side of the tooth of the worm inquestion. The other side is determined by laying out the points S, U andV in like manner. V i The contours of the projection'of thecorresponding tooth of the hob is now laid out on the ellipses M, LandKrepresenting the hob in Fig. 12. The procedure is similar to thatpursued with the worm." Thus, referring toFig. 11,the distance from z'toa is measured and is then transferred to Fig.1.? l

85 by the'plane OF 17 and, as this plane is and is laid-off on theellipse M from the point z", and this gives the location of the point a.Similarly, the distance ig (Fig. 11) gives on Fig. 12 the point 9. 'Andthe distance ir on Fig. 11 gives 1' on Fig. 12; The remaining points p,s, u and 'v are likewise ascertained, and smooth curves, which arenearly straight, are drawn through these points.

The same procedure is followed until sufficient sections have been laidout; giving the entire series shown by Fig. 12.

This having been done, it will be seen that,

at regions indicated by black in Fig. 12.

there is an overlapping'and that interferences exist at suchplace. Itwill be noted, however, that with respect to the last four teeth thereis no appreciable interference, and also that in no case does anyinterference exist on both sides of the cutting-edge, but always on thesame side. This is interpreted to mean that the last four teeth F19,F18, F17 F16, (the ones last acting to cut) need no deformation but maybe preserved intact in the hob and used as finishing teeth. Also, Fig.12, makes it clear that by merely re cutting the helicoid of the hob onone side only, using a lead somewhat longer than the regular lead-of thehob, all interfering 'portions will be eliminated; it being a simplematter to compute the auxiliary lead since, by measuring the blackregions, the precise maximum amount to be removed for each tooth isreadily ascertainable.

In this way, there is obtained a non-interfering helicoid;each side ofwhich (byreason of being a uniform helix though of different lead fromthe other side) can be very easily and accurately out by ordinarymachine tools without involving the complications arising from any hobdesign based on.

non-uniform or variable helices. By gashing and relieving this helicoidat appropriate points, there will be formed such cutting edges as may bedesired, and the thus-formed hob, will accurately reproduce thepredetermined worm. 7

It is to be noted that, in a hob thus formed, the labor or cutting willnot be distributed to the best advantage among the various teeth,inasmuch as the successive cuttingedges would follow Indian-file in thepath of the pioneer edge and the burden of the work of cutting the pathwould, to an excessive degree, fall upon the advance. teeth; to

the great disadvantage of the quality of the tooling operation and tothe injury and rapid deterioration of the hob. I

Now this invention also affords a remedy for the aforesaid obstacle tothe processing of a worm by a hob in which all the teeth aresubstantially identical. 1 Instead of presenting identical cutting-edgesin succession to the helical path of the worm, my method proposes theuse of teeth of different sizes so graduated that the labor will bedistributed among the various teeth in proportion to the finishingoperation, but a dual-capacity hob combining in full measure both thesequalities. In other words, each revolution 1 of my hob not only cutsaway a considerable amount of "material (corresponding to a socalledroughing operation) but also produces a substantially infinitesimalaccurate facet not only accurately located incoincidence with theenvelope of the predetermined worm-helix, but also presenting a surface.well-finished accordingto the standards of a finishing cutter. Thesefacets in the aggregate compose the smooth continuous surface of theultimate helix of the worm andthis surfaceis equal,iif not superior, tothat vproducedby a conventional disk-cutter; tho at a far greater speedand consequently at a much lower cos. .7 a The structural nature of thesupplemental improvement over my previously disclosed primary invention,will be understood by referring to Figs. 1;.to 3, inclusive.

' It will be noticedthat the first-actingcutting-edge T1 has had a veryconsiderable portion of its crown removed (without alter-g ing the sidesof the helicoid) with the result that this tooth 'will' make only ashallow cut into the blank. The nextcutting tooth T2 has somewhat lessof its crown removed so thatit will; cut a little deeper into the blankand, since it follows directly in the path of tooth T1, the amount 'ofmaterial removed by it will be approximately the same as that.previously removed by the advanced tooth; This successive alterationiscarried throughthe variousteethuntil somenot been reduced, andwhich may,therefore,

be regarded as a finishing tooth sinceits normal section responds tothat shown by Fig. 9; likewise several, subsequent teeth,

such as F17, F18 andF19, are also unaltered.

It is to benoted that, beginning with tooth F16, the side wall of"thehelicoid. has been reduced by employing the auxiliary lead, as

previously described, so that no interferences will be produced by anyof the advanced roughing teeth. This rectification ofl the helix may ofcourse, within the spirit'of theinventiombe developed on both sides "ofthe tooth, as shown by dotted lines on Fig.

2, in which (event,; as a concomitant, the teeth will have a progressivecutting effect on both sides-thereof. The removal of metal from both.sides of the so-called roughing teeth is likewise clearlyrepresented byFig. 12 the heavier lines indicating the final contour" to be giventhose teeth and thelighter lines on both sides of the ultimate contour,and spaced away therefrom, being the original contours. It will likewisebe understood that it is not essential, in thus resorting to-auxiliaryleads, to remove only suitici'ent metal to avoid interferences, inasmuchas the removal of somewhat greater amounts of metal from the interferingside of the hob willmerely have thereifect of varying the distributionof the duty amongthe teeth; leaving the-ultimate cuts to be made, asbefore, by the finally-acting undistorted tooth or teeth employed solelyfor finishing cuts as 'distinguished from roughing cuts. The crowns ofthe latter are preferably reduced uniformly beginning'with tooth T15 sothat the peaks of their cuttingedges may be said to 'liein a spiralpath. Certain of the adv vanced roughing teeth, as shown by Fin. 2,

have their peripheries-provided with notches, N,* thusbreaking up thechip and enabling ,ing tooth F16. or to'one of the other finish-yingjteethas F19, for assistance in mounting tionswithout omittingcertain features that, i from the standpoint of the prior art, fairlythe hob in the" hobbing machine preparatory to or during the'cutting ofthe worm.

,Without further analysis, the foregoing will so fully reveal the gistof the invention that others can, by applying current knowledge, readilyadapt it for various utilizaconstitute essential characteristics of thegeneric or specific aspects ofthis invention, and therefore suchad'apt'ations should be and are intended to be comprehended withinthe-meaning and range-of equivalency of the followingclaimsr I 7 Having.thus revealed this invention, vI claimeas new and desire to secure byLetters Patent ofthe United States p 1., The art of continuously andprogressively producing a finishedhe'licoidal contour by anon-intermittent operation consisting in cyclically presenting to thework'in rapid succession a series of cutting-edges each having anarcuatemotion and arranged progressively to act in the path of theimmediatelypreceding cutting-edge and to remove about 1 the same amountof materialas said imme-v diately-preceding edge, and simultaneouslyeffecting a rectilinear feeding motion between the work and saidcutting-edges par'allel iwith the axis of the work to produce ahelicoidr 2. A process for continuously forming a helical groovehaving apredetermined contour consisting in consecutively removing from the endregion only of said groove a .succession of under-sized cutsprogressively in creasinginzsize to that of the said contour as a limit,and repeating said cycle whilesimul-i to, carry the finished portions ofsaidzgroove beyond the region of operations duce a helicoid.

3; A process of hobbing a worm close 'toa shoulder consisting inemploying a disk-like hob having but few convolutions and providing aconsiderable number of roughing-cutting edges arranged in a spiral pathand several finishing-cutting-edges arranged in a trulyfhelical path;mounting said hob so that its'axis lies at a sharp. non-intersectingangle with the axis of the-blank; rotating both said blank and said hobtoproduce a relativemo so as to pro tion betweensaidhob andblank;andldiscontinuing said feed before said disk-like hob comes into contactwith the shoulder of said blank.

4. A generative method of converting a cy lindrical blank into aowormwhich consistsin taining said disk-likehob that its axis is set at anangle to the plane containing both the axes of the blank and the lineperpendicular 1 to both of said axis; causing both said hob and saidblank to rotate and simultaneously effecting a relativefeed inarectilinear direc-v tion, whereby the cutting edgesv of saidhob mayprogressively-generate a helical groove in-the periphery of said blank.

5. A worm generating process consisting in employing a hob having amultiplicity of cutting edges arrangedin a convoluteseries, the

successivecutting edges each extending in op eration slightly outside ofthe path of opera- 13 tion of its predecessor; maintaining saidhob inintersecting relation with the periphery of a cylindrical blankand withits axis nearly parallel with 'the axis ofsaid blank; and

s multaneously rotating bothsaidhob and"? 7 blank while bodily feedingsaid hob along a path parallel with the axis of-saidblank.

i 6. A generative method" of converting a cylindrical blank into a wormwhich consists in employing a disk-like hob presenting a '12.

plurality of roughing-cutting-edges coincident with a tapered spirallocus extending-in a convolute direction and several finishing-1 cuttingedges coincident with a truly helicai locus *so maintaining saiddisk-like hob that 7. The art of continuously and progres sivelyproducing a finished helicoidal contour by a non-intermittent operationconsisting in cyclically presenting to the work in rapid successionfirst, in a tapered spiral, a

. series of roughing-cutting-edges and then,

in a truly helical path a series of finishingcutting-edges, the axes ofthe spiral and helical cutting-edges being coincident and set at anangle to the axis oi the work, and simultaneously effecting arectilinear feeding motion between the work and said cutting-edgesparallel with the axis of the work'to produce the helicoidal contour. i1 p 8. A generative method of converting a cylindrical blank into a wormwhich consists in employing a disk-like hob presenting a successlon ofcutting edges coincident with a tapered spiral locus extending throughabout one convolution; so maintaining said disklike hob that itsaxis isheld at an angle of a few degrees to the plane containing both the axisof the blank and the line perpendicular to both of said axes; causingboth said hob and said blank to rotate and simultaneously eflectingarelative feed in a rectilinear direc: tion, whereby a considerablenumber of the advance cutting edges of said hob may progressively takedeeper cuts and generate a helical groove in the periphery of saidblank.

9. A method of converting a cylindrical blank into a helical gear whichconsists in employing a disk-like hob presenting to the blank cuttingedges coincident with a tapered spirallocus extending in a convolutedirection; so maintaining said disk-like hob that the axis is set at anangle to the plane containing both the axis of the blank and the lineperpendicular to both of said axes; causing both said hob and said blankto rotate and simultaneously effecting a compatible relative feed ina'rectilinear direction, whereby the cutting edges of said hob mayprogressively act to generam a helical groove in the periphery of theblank.

10. The method of converting a cylindrical blank into a gear with teethof predetermined contour which consists in employing a disk-like hobhaving teeth arranged in a thread and progressively increasing in widthto thereby present a ser es of roughing teeth followed b r afull-sizedfinishin tooth so maintaining said hob that the axis is anangle. to the plane conta ning both the axis of the blank and the lineperpendicular to both of said axes; simultaneously rotat ng both saidhob andblank while in continuous engagement and effecting a relativefeed in a direction parallel to the axis of the blank wherebysuccessive'hob teeth out outside the path of the preceding tooththroughout the extent of the side cuts on the gear teeth and the geartooth spaces are progressively increased in size to said contour as alimit.

11., The method of forming helical tooth spaces of predetermined curvedcontour in suitable gear. blanks which consists in utilizing a hobhaving a series of teeth arranged in a thread and progressivelyincreasing insize both as to width and height to present a series ofroughing teeth followed by a finishing '3 tooth, and effecting asimultaneous compatible rotation of the blank and hob and a relaT tivezfeed while in continuous engagement, and causing said series of teeth topass through a gear tooth space of-the blank in each revolution ofthehob to effect a series i of cuts progressively increasing in size tothe contour of the desired gear tooth as a limit. 12. The method ofconverting a cylindrical blank intoa gear with teeth of predeterminedcontour in a continuous operation which consists in cyclicallypresenting to the blank in rapid succession and in an arcuate directiona series of cutting teeth, including afinishing tooth, adapted to act inthe path of thepreceding tooth and to successively cut outside athepathof the. preceding tooth I throughout the extent of the respective sidecuts on the gear teethwhile simultaneously effecting a compatiblerotation 'ofjsaid blank C5100 and'arel'ative feed between the blank andcutting edges parallel to the axis of the blank thereby to enlargeprogressively the gear tooth space to the predetermined-contour and toadvance said contour along the blank.

' '13. The method of forming suitable cylindrical blanks into gears withhelical teeth of predetermined contour and having opposed side facesinclined with respect to aplane perpendicular to the axisot the blankwhich consists in employing a hob having a series of teeth arranged in athread with the cutting profilesof the respective hob teeth disposed atprogressively greater widths, effecting compatible simultaneous rotationof the hob an; and blank and a relative .feed in the direction of theaxis of the blank while maintaining 'the ax is of the hob at an angle tothe: plane containing the axis of the blank and the line perpendicularto both of said axes tocyclic- 32*;

allyefiecta series of cuts in the region op erated on progressivelyncreasing'in s ze to saidpred-etermined contour as a limit,

l-lQThe' method'of form'ing gears with teeth ofcurvedcross-sectionalcontour with 1 a simultaneously simultaneouslyeffecting-a feed therebetween parallel with the axis of the blank andcansing the said teeth to pass through a tooth space of the blank ineach revolution of the hob whereby the respective teeth progresrotatinggear blank and to advance said. contour in ahelix along the blank Inwitness whereof, I hereunto subscrilie my name.

' I WILLIAM F. ZIMMERMANN.

sively cut away the gear tooth spaces by a 7' series of cutsprogressively-increasing in size.

1 5., The art of continuously and progres-' sively' forming a helicalgear having a predetermined gear tooth contour which consistsincyclically presenting to the gear blank in rapid succession and along apredetermined helix relative to the blank a series of v of theimmediately preceding tooth but eX- cutting-edges progressivelyincreasing in size each having an arcuate motion and arranged andoperated progressively to act in vthe patlr tending outside thereof.thesuccessive cuts series of cutting teeth progressively increasingnsize each having an arcuate motion and predetermined helix relative tothe blank a i arranged progressively to act in the path of theimmediately preceding. tooth and to remove about the same amount ofmaterial as a said immediately preceding tooththe sucr cessive cutsprogressively increasing in size the path of the preceding tooth, saidcutting Q edges comprising first a series ofroughing to the contour ofthe desired worm gear tooth asalimitv V .7 7' I 17. The art ofcontinuously and progressively forming helicalteeth of predeterminedfinished contour on suitable gear blanks {which consists in cyclicallypresentingtothe gear blank in rapid succession and along a predeterminedhelix relative to the blank a series of cutting edges each having'anarcuate motion and arranged and operated to act 1n edges progressivelyincreasing in size to produce a series of cuts correspondinglyincreasing in sizeand then a series of finishing cutting edges ofthesame size coincident'with a truly helical. locus. i

The method of converting cylindricalgear blank into a worm gear withteeth of predetermined contour in a continuous opera tion which consistsin cyclically presenting 'to the blank in rapid succession and in anarcuate direction a series of cutting edges adapted'to act in the pathof the preceding icutting edge and to successively produce a wider anddeeper cut while simultaneously effecting a compatible rotation of saidblank and relative feed between the'blank and cut ating edges parallelto the axis of the blank thereby to enlarge'progressively the gear toothspace to the predetermined contour and

